Wearable Breast Pump Sizing: E10, E20, and S1 Insert Guide
By eufy - Built with Care | Home Security System & Robovacs | Published: 2026-10-15
Category: Tips & Care
Learn how to size a wearable breast pump flange, when to switch inserts, and how the eufy 17 mm sizing insert fits E10, E20, S1, and S1 Pro pumps.
Quick answer
Measure your nipple diameter in millimeters, then choose the insert size closest to that measurement without going smaller. For eufy wearable pumps, the 17 mm sizing insert is one option in the E10, E20, S1, and S1 Pro system. Recheck the fit whenever pumping feels painful, output drops, or your nipple size changes during breastfeeding stages.
Why the right insert size changes your pump session
A flange that is too large pulls in extra areola tissue, which can cause pinching, swelling, and uneven milk removal. A flange that is too small rubs the nipple walls and restricts milk flow. The insert sits inside the flange and narrows the tunnel to match your nipple, so the pump can create a better seal with less tissue trauma.
Nipple size is not fixed. It can change between the early postpartum weeks, established breastfeeding, and weaning. eufy notes that nipple size may change during different breastfeeding stages, which means the insert that worked in month one may not be the right one in month four.
How to measure before you order
Measure at the base of the nipple, not the tip. Use a soft tape or a printable ruler and check the diameter in millimeters. Measure both sides, because one breast can be slightly larger than the other. If you are between two sizes, start with the larger insert and adjust down only if you see persistent areola pulling.
eufy provides a sizing guide to help you select the right size for optimal comfort. Use that guide alongside your own measurement rather than guessing from bra size or pump brand alone.
When to replace or switch inserts
eufy recommends replacing flange inserts periodically, and the 2-pack format makes it easier to keep a spare on hand. Switch sizes if you notice a ring of areola being drawn into the tunnel, if pumping becomes painful after the first minute, or if output drops without another explanation. Keep the old insert only as a backup, not as your daily fit.
Step-by-step insert sizing routine
- Measure both nipples in millimeters: Measure at the base of the nipple, not the tip, and write down both numbers. Common mistake: measuring once and assuming both sides match. Checkpoint: if the two sides differ by more than 2 mm, size each side separately.
- Compare your measurement to the eufy sizing guide: Use the eufy sizing guide to match your measurement to the closest insert size. Common mistake: choosing a size based on what a friend uses instead of your own measurement. Checkpoint: if you are between sizes, start with the larger insert.
- Install the insert into the flange: Press the insert evenly into the flange tunnel so it sits flat with no folded edges. Common mistake: forcing a wrinkled insert, which breaks the seal. Checkpoint: run a finger around the rim to confirm the insert is seated evenly.
- Test the fit during a full pump session: Center your nipple in the tunnel and pump for several minutes. Common mistake: judging the fit in the first few seconds before the pump reaches its rhythm. Checkpoint: you should see nipple movement without a ring of areola being pulled in.
- Recheck at each breastfeeding stage: Measure again if pumping becomes painful, output drops, or your breasts feel engorged after a session. Common mistake: keeping the same insert for months without rechecking. Next step: keep the eufy 17 mm Sizing Insert 2-Pack as a spare option and replace worn inserts as eufy recommends.
Product facts
- eufy 17 mm Sizing Insert (2-Pack) for Wearable Breast Pump E10/E20/S1/S1 Pro: eufy 17 mm Sizing Insert (2-Pack) is compatible with eufy Breast Pump E10, E20, S1, and S1 Pro. If you own any of these four pump models, this insert is a direct fit and does not require a separate adapter.
- eufy 17 mm Sizing Insert (2-Pack) for Wearable Breast Pump E10/E20/S1/S1 Pro: The insert is HSA/FSA eligible and comes in a 2-pack. You can use pre-tax health dollars and keep a spare insert ready while one is in use or drying.
- eufy 17 mm Sizing Insert (2-Pack) for Wearable Breast Pump E10/E20/S1/S1 Pro: eufy recommends referring to the sizing guide and replacing flange inserts as needed. Sizing is not a one-time task; plan to recheck fit as your breastfeeding stage changes.
